Structural magnetic and dielectric studies on cobalt based ferrite nanoparticles

Abstract

The thesis describes the structural, magnetic and electrical studies of nickel and bismuth substituted Co-Zn ferrites and cadmium substituted Ni-Co ferrite. Co0.5-xNixZn0.5Fe2O4(x = 0.0, 0.1, 0.2 and 0.3) were prepared by co-precipitation method. The average particle size determined from XRD using Scherrer formula were found to decrease for the nickel concentration x = 0.1 and increases for the concentrations x = 0.2 and 0.3. The average particle size recorded from TEM image for the Ni concentration x = 0.2 matches with the values obtained by XRD. The average cation distribution and its variation with composition for as prepared and sintered samples were determined by using the X-ray intensity formula. It is observed from the as prepared and sintered samples that there is a deviation from the normal cation distribution among the tetrahedral (A) site and octahedral (B) site leading to a metastable state. The analysis of particle size through TEM image matches well with the XRD analysis for the cadmium concentration x = 0.2. From X-ray diffraction studies the distribution of cations in A-site and B-sites have been deduced and it has been noted that the lattice constant was found to increase with addition of Cd2+ concentration in Ni-Co ferrites. The saturation magnetization was found to decrease with increase in cadmium concentration for all the samples. The hysteresis loop for the concentrations x = 0.0, 0.1 and 0.3 shows almost zero coercivity and remanance at 300 K; hence, the samples behaves as superparamagnetic at 300 K; whereas for the concentration at x = 0.2 the coercivity is found to be 32 Oe, at 300 K. The dielectric measurements were carried out in the NixCo(0.5-x)Zn0.5Fe2O4 system over the temperature range from 300 to 700 K as a function of frequency from 50 Hz to 5 MHz. The variation of dielectric constant and dielectric loss factor for the prepared sample is explained on the basis of Maxwell-Wagner interfacial polarization. newline